This invention relates to a proportional control valve for operating a larger main valve. More specifically, the invention provides for opening or closing a control valve in varying degrees and maintaining the control valve in a fixed partially open state, in addition to being able to fully open and fully close the control valve.
It is known in the art to open and close a main valve by mounting, on its actuator, a control valve of the rack and pinion opposed-piston type. In such control valves, each of two pistons is provided with a rack that engages one or more coaxially mounted pinion gears. As the pistons are translated away from one another, their racks rotate the pinion gears in one direction. As the pistons approach one another they rotate the pinion gear in the opposite direction. An example of such a control valve is sold under the logo Dynamite F-790.
Movement of the pistons is accomplished by applying positive air pressure to a space between the pistons to force them apart while relieving the pressure outside the region between the pistons. Conversely, the pistons can be forced to move toward one another by relieving the pressure between them and increasing the pressure in the region outside the space between the pistons.
Prior art control valves are operated in a fully open or fully close state depending upon whether the chamber between the pistons is pressurized or evacuated. Such prior art control valves cannot reliably be used to partially open a main valve to a predetermined degree and maintain the degree of openness once achieved.